In the Federal Republic of Germany, wind turbines are deemed by law to be building structures, the engineering design, erection and operation of which are supervised by the building permit offices of the separate states and by the locally competent building authorities.
The competent authorities require above all that wind turbines, and especially their rotor blades and mechanical engineering components, be monitored at periodic intervals to maintain their operational safety. Irrespective of such requirements, regular maintenance and repair are essential for maximum availability of wind turbines.
In the first years of wind power use, telescopic platforms or so-called aerial platforms, mounted on trucks, were used for inspecting, maintaining and repairing rotor blades.
Owing to the rapid increase in the hub heights of wind turbines, and based on many years of experience in cleaning building facades, intensifying use of wind energy in Germany led to modified and hoistable types of suspended access equipment (SAE) being developed. Examples of such suspended access equipment are described in some patents, patent applications and utility models. What is common to all these solutions is that inspection, maintenance and repair work is performed on a rotor blade pointing vertically downward. The rotor is successively rotated so that all the blades can be treated.
The increasing size of wind turbines, not only with respect to hub height, but also to the specific dimensions of the blades, combined with the desire for offshore wind power generation gives rise inevitably to requirements for suspended access equipment that cannot be met or fully met with the construction designs that have existed hitherto. To perform inspection, maintenance and repair work on all the blades of a wind turbine as efficiently as possible, it is necessary to select mountings for the suspended access equipment such that the rotor can still be rotated when the access equipment is suspended. The disadvantage of suspending the access equipment from the rotor blades themselves is that, in order to treat the next rotor blade, the suspended access equipment must be dismounted and remounted again after the rotor has been rotated to the next position. If repair work needs to be carried out in sections where the mounting for the suspended access equipment is located, this type of mounting is doubly unfavorable. Since maintenance and repair work on blades mainly involves lamination and painting work, dismounting and remounting suspended access equipment cannot be carried out until after full hardening, for example of the paint finish, in the area of the mounting.
Current suspended access equipment that is not suspended from the rotor blades themselves, but from the machine house instead have the disadvantage that, although the rotor can still be turned while the suspended access equipment is mounted, it is necessary to release the tension in guy lines to the ground. For offshore applications, such solutions are out of the question, of course.
What is common to all solutions hitherto is that the suspended access equipment lacks the flexibility to adapt to changes in the cross-sectional profile of the workpiece (in this case the blades) during operation.
The bigger rotor blades become, the greater the flange diameters and the greater the maximum blade depth become. The blade tips, etc., and above all their blade thickness, remain approximately the same, in contrast—irrespective of whether the blade is 20 meters or 40 meters in length. The consequence is that the rotor blades can be treated very well in the flange area or in the upper third next to the hub, whereas work becomes increasingly difficult to perform the closer one gets to the blade tip. The reason for this is the increasing gap between the rotor blade or workpiece surface and the closest front handrail (as defined in the DIN EN 1808 standard) of the suspended access equipment, which is limited to a major extent by the distance that personnel can reach.